Animals don’t have reason or moral accountability but there is abundant evidence that mammals and birds have feelings. And feelings often follow their own rules. A cat may adopt a duckling, under the right circumstances or a lioness may adopt an oryx.
So what would cause animals to put territorial or predatory instincts aside?
[Evolutionary anthropologist Isabelle Catherine] Winder and [anatomist Vivien] Shaw suggest several factors, including
- Domestic animals, fed and protected by humans, are free to indulge mothering or protective instincts. They may not even take note of differences between species.
- Among wild animals, the urge to nurture may overcome other urges…
- In large herds, adoption of an orphan may give young females practice with nurturing. It’s relevant, perhaps, that the young are usually only with an adoptive parent for one season anyway.
If we don’t feel a need to affirm kin selection theory or selfish gene theory, maybe we don’t need an explanation — “evolutionary” or otherwise — for animals adopting unrelated animals. Animals think with their feelings, which do not always follow the theory. If whatever they are doing doesn’t kill them or their kind, that’s enough.